(1) Field of the Invention
The invention relates to antennas, and more particularly to slotted antennas having cones attached to the slots for radiation to free space.
(2) Prior Art
In Griffith Pat. No. 3,605,099, a plurality of devices is shown attached to a radiating antenna at slots formed in the outer conductor thereof. Each device comprises a tapered disc, formed as a triangle of revolution. Opposing halves of two adjacent devices form frustoconical reflecting elements for a radiating slot included therebetween. A coaxial transmission line having half-wavelength wide slots is utilized in '099, and the frustoconical elements are specifically required to be at least one wavelength in length, and preferably one and one-half wavelengths. The apparatus further requires specific elements, comprising probes 36 with universal joints 38, for matching the antenna transmission to the free space.
The present apparatus provides for a set of cones attached to a slotted antenna, but eliminates the requirement of such special matching elements. The present disclosure specifically provides for cones having quarter wavelength radii, whereby the cones act as impedance transformation devices for transforming the load impedance seen by the slot in the antenna to the impedance of free space.
A fundamental disclosure of a double cone antenna is found in Carter U.S. Pat. No. 2,175,252. Both bi-cone antennas and disc-cone antennas are disclosed in '252. However, no consideration is given to impedance matching as is contemplated in the present invention, or to the use of plural slots and varying cones as contemplated herein. Cones having a length of 0.23 wavelength are shown in '252 as one possibility, but this appears to be as a means for presenting substantially a resistance at the apices of the cones, and not to enable impedance matching of a specific load to a specific line.
Bradley U.S. Pat. No. 2,471,021 shows a slot cone antenna using a resonant cavity with a slotted cavity wall. Devices appearing to provide conical shapes are attached to the outer wall, but no consideration is given to the radial length of the cones to provide matching characteristics for the antenna. Use of a quarter wavelength cone in the present structure avoids the need of the resonators of '021.
Chu U.S. Pat. No. 2,486,589 discusses problems with the Carter '252 antenna, and provides improvement by shaping the antenna in the form of an apple core. Buchwalter et al U.S. Pat. No. 2,455,224 ulilizes a cylindrically shaped antenna having spaced annular regions of discontinuity, and provides flanges in the discontinuity spaces. No contemplation of the use of cones in the presently disclosed combination is found in either reference.
In summary, none of the prior art disclosures known to the inventor, singly or in combination, suggest the present invention as hereinbelow described and claimed.